Unable to build .ipsw file

I am trying to jailbreak my 2.1 ipod touch and when I'm in Pwnage Tool I get the error message "failed to build custom .ipsw file" after it says in the log that it failed to detach the restore ramdisk from '/Volumes/ramdisk.' What does that mean and could anyone help. I have already spent hours trying to find help, and have tried both Pwnage Tool and QuickPwn (the latest versions) on my MacBook. Please could someone help. I have already spent 50 dollars on a touchmods mic so I can run SIP-VOiP on my touch, so I urgently need all the help I can get.